In an RF receiver, intermodulation distortion is caused by an interfering signal of sufficient signal strength mixing with a local oscillator (or injection) signal that results in an undesired signal appearing in the passboard of a receiver's intermediate frequency (IF) section. Generally, a desired signal is also mixed into the IF passboard, and the comtemporaneous presence of the undesired signal distorts the desired signal thereby reducing the intelligibilty of the desired signal.
It is known that the third order IM distortion of a balanced commutation mixer may be represent by: ##EQU1## Where, IM is the third order intermodulation distortion;
V.sub.c is the peak-to-peak local oscillator voltage; PA0 V.sub.s is the peak received signal voltage; PA0 t.sub.r is the rise (and fall) time of V.sub.c ; and PA0 f.sub.lo is the frequency of the local oscillator.
As is known, the peak received signal voltage (V.sub.s) may be viewed as a random parameter, and the frequency of the local oscillator (f.sub.lo) is typically determined by the frequency of the desired signal Accordingly, for a given received signal level and frequency, analysis of equation (1) reveals that the IM of the mixer (and thus the receiver) may be minimized (theoretically to zero) by increasing the peak-to-peak local oscillator voltage (V.sub.c), or by reducing the rise (and fall) time of the local oscillator waveform (t.sub.r), such as by using a square wave. However, signal amplification and square wave generation require high current to enable active devices to operate at high speed. Thus, this practice may be detrimental to battery powered RF receivers since the radio's operational lifetime may be reduced to an impractically short interval. Conversely, merely adding more batteries (or cells) to an RF receiver may so increase the weight and physical size of the receiver as to make it undesirable to the comsuming public.